Flow control valve

ABSTRACT

A constant-flow valve assembly having a first passageway carrying fluid at a first pressure, a piston chamber, and a second passageway connected to the chamber and carrying fluid at the second pressure. A third passageway carries fluid at a third pressure. An adjustable valve is between the chamber and the third passageway, and an adjustable restrictor is positioned between the first and second passageways. An inlet portion of the restrictor assembly receives fluid at the first pressure and directs the fluid to a restrictor, and outlet portion directs the fluid to the second passageway at the second pressure. The restrictor is movable to adjust the position of entry and exit portions relative to the inlet and outlet portions to adjust a fluid flow rate to the second passageway to adjust the flow rate through the valve assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 12/838,316, filed Jul. 16, 2010 and titled FLOW CONTROL VALVE, whichis a continuation of U.S. patent application Ser. No. 11/741,477, filedApr. 27, 2007 and titled FLOW CONTROL VALVE, which claims priority toand the benefit of U.S. Provisional Patent Application No. 60/795,748,filed Apr. 27, 2006 and titled FLOW CONTROL VALVE, each of which arehereby incorporated herein by reference thereto.

TECHNICAL FIELD

This invention relates to generally constant flow control valves. Moreparticularly, several aspects of the invention are directed towardvalves that maintain a substantially constant flow despite changes inthe pressure drop across the valve.

BACKGROUND

In the production of oil and gas, chemicals such as corrosioninhibitors, scale inhibitors, paraffin inhibitors, hydrate inhibitors,and demulsifiers are typically injected into the wells to maintainefficient flow of oil or gas. These chemicals usually need to be addedto the wells production at a constant rate. Often one pump is used toinject the same chemical into several wells with the use of pressurecompensated rate control valves at each injection point. The use ofthese rate controllers reduces set up and operating costs of injectionsystems because the alternative is to install a separate pump for eachinjection point and to maintain several pumps instead of one. Theseinjection valves must be pressure compensated because they need tomaintain a rate set point with changes of several thousand pounds persquare inch across them to accommodate fluctuations in well pressure. Atypical chemical injection rate for an oil well is between 0.5 to 200 USgallons per day. Injection pressures range between 500 to 20,000 psi.

The most robust method to date to achieve rates in this range usingpressure compensated rate controllers is to govern the pressure dropacross a fixed orifice. The set point for this method is changed byvarying the pressure drop across the orifice. This method is describedin U.S. Pat. No. 4,893,649. Previous methods to vary the area whilemaintaining a constant pressure drop have not adequately worked in thelow flow range because passages created by mating needles and trims ormating threads to restrict flow are often less than 0.001 inches wide,which makes them prone to clogging and/or filming. The fixed orificemethod is robust since hole passage can be made to pass the largestdebris for a given flow area and several holes cascading in series canbe used to give the same resistance with as much as a twenty foldincrease in the flow area reducing the filming and clogging tendencies.The consequences of varying the pressure drop across a fixed resistor isthat the range of flow rate set point is limited and passages cannot beopened up to pass blockages as can be done with a mating needle andtrim.

Set point range of a valve is defined by its “turn down,” which equalsthe valve's highest flow rate divided by the lowest flow rateachievable. For a fixed valve orifice, the turn down is calculated bytaking the square root of the highest pressure drop across the orificedivided by the lowest pressure drop. For example, a valve that offers apressure drop across the orifice of 200 psi at maximum flow and 2 psi atminimum flow will have a turn down of 10:1. During the life of the wellthe flow rate range may need to be adjusted, which involves replacing anorifice. Sending personnel or equipment to remote locations to change anorifice represents a substantial expense, particularly if the valvelocation is under water.

SUMMARY

A constant-flow valve assembly is provided that overcomes drawbacksexperienced in the prior art and provides other benefits. In oneembodiment, a constant-flow valve assembly comprises a first fluidpassageway configured to carry fluid at a first fluid pressure, achamber having at least a portion configured to receive fluid at asecond fluid pressure less than the first fluid pressure; and a secondfluid passageway connected to the portion of the piston chamber andconfigured to carry fluid at the second fluid pressure. A third fluidpassageway is configured to carry fluid at a third fluid pressure lessthan the first and second fluid pressures. A piston is slideablydisposed in the chamber, and an adjustable valve member is providedbetween the chamber and the third passageway.

The adjustable valve member is configured to provide a substantiallyconstant fluid flow to the third passageway substantially independent ofthe pressure differentials between the second and third fluid pressures.An adjustable restrictor assembly is between the first and second fluidpassageways. The restrictor assembly has an inlet portion, an outletportion, and a restrictor with a fluid pathway extending therebetween.The inlet portion is positioned to receive fluid at the first fluidpressure from the first fluid passageway and to direct the fluid to therestrictor. The outlet portion is positioned to receive fluid from therestrictor and direct fluid to the second fluid passageway at the secondfluid pressure. The restrictor has an entry portion and an exit portionof the fluid pathway. The restrictor is movable to adjust the positionof the entry and exit portions relative to the inlet and outlet portionsto adjust a fluid flow rate of fluid through the fluid pathway to thesecond fluid passageway, thereby adjusting the flow rate through thevalve assembly.

In another embodiment a constant-flow valve assembly comprises a firstfluid passageway with fluid at a first fluid pressure, a chambercontaining fluid at a second fluid pressure less than the first fluidpressure, and a second fluid passageway connected to the portion of thechamber and containing fluid at the second fluid pressure. A third fluidpassageway has fluid at a third fluid pressure less than the first andsecond fluid pressures. A piston is slideably disposed in the chamber. Abiased valve member having a biasing member and a valve body is coupledto the piston. The valve body is positioned between the chamber and thethird passageway and configured to provide a substantially constantfluid flow to the third passageway substantially independent of pressuredifferentials between the second and third fluid pressures.

A restrictor assembly is between the first and second fluid passageways.The restrictor assembly has a first sealing pad, a second sealing pad,and a restrictor with a fluid pathway extending therebetween. The firstsealing pad is positioned to receive fluid at the first fluid pressurefrom the first fluid passageway and to direct the fluid to therestrictor. The second sealing pad is positioned to receive fluid fromthe restrictor and direct fluid to the second fluid passageway at thesecond fluid pressure. The restrictor is movable to adjust the positionof the fluid pathway relative to the inlet and outlet portions to adjusta fluid flow rate of fluid through the fluid pathway to the second fluidpassageway, thereby adjusting the flow rate through the valve assembly.

Another embodiment provides a constant-flow valve assembly thatcomprises a body portion having a first fluid inlet, a piston chamber,and a first fluid outlet. The first fluid inlet receives fluid at afirst fluid pressure. The piston chamber has a first portion exposed tothe fluid at the first fluid pressure and has a second portion exposedto fluid having a second fluid pressure less than the first fluidpressure. The first fluid outlet is configured to carry fluid at a thirdfluid pressure less than the first and second fluid pressures. A pistonis slideably disposed in the piston chamber. A seal in the pistonchamber between the piston and the body separates one portion of thefluid at the first fluid pressure from another portion of the fluid atthe second fluid pressure. A valve member is coupled to the piston inthe second portion of the piston chamber and is configured to provide asubstantially constant fluid flow from the second portion of the pistonchamber toward the outlet substantially independent of the pressuredifferentials between the first, second, and third fluid pressures.

A first fluid passageway is connected to the first portion of the pistonchamber and configured to contain fluid at the first fluid pressure. Asecond fluid passageway is connected to the second portion of the pistonchamber and configured to contain fluid at the second fluid pressure. Anadjustable restrictor assembly is coupled to the body between the firstand second fluid passageways. The restrictor assembly has a second inletportion, a second outlet portion, and a restrictor body with a fluidpathway extending therebetween. The second inlet portion is positionedto receive fluid from the first fluid passageway. The second outletportion is positioned to direct fluid to the second fluid passageway.The restrictor body has an entry portion and an exit portion of thefluid pathway, the restrictor body is movable relative to the secondinlet portion to adjust how much of the entry portion is uncovered bythe second inlet portion to receive fluid directly therefrom and howmuch of the entry portion is covered by the second inlet portion torestrict a flow rate through the entry portion to the exit portion,thereby adjusting the flow rate through the valve assembly independentof the differences in the first, second, and third fluid pressures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a constant flow valve assembly inaccordance with an embodiment of the present invention.

FIG. 2 is an enlarged schematic cross-sectional view of the valveassembly taken substantially along lines 2-2 of FIG. 1.

FIG. 3 is an enlarged cross-sectional view of a portion of the valveassembly where indicated in FIG. 2 and showing a restrictor assembly.

FIG. 4 is an enlarged isometric view and partial cutaway view of ageometry of a hollow cylinder and sealing pad shown removed from therestrictor assembly of FIGS. 2 and 3 and shown in an open-mostcondition.

FIG. 5 is an enlarged isometric view and partial cutaway view of thegeometry of the hollow cylinder and sealing pad of FIG. 4 and shown in areduced flow position.

FIG. 6 is a schematic cross-sectional view of the valve assembly inaccordance with another embodiment of the invention.

FIG. 7 an enlarged cross-sectional view of a portion of the valveassembly where indicated in FIG. 6 and showing a restrictor assembly.

FIG. 8 is an enlarged isometric view and partial cutaway view of thegeometry of a hollow cylinder and sealing pad shown removed from therestrictor assembly of FIGS. 6 and 7 and shown in the open-mostcondition and all flow through the receptacles and channels bypassed.

FIG. 9 is an enlarged isometric view of cascading notches and channelsin the hollow cylinder of FIG. 8, with the sealing pad removed forpurposes of clarity.

FIG. 10 is an enlarged isometric view and partial cutaway view of thegeometry of the hollow cylinder and sealing pad of FIGS. 6 and 7 and ina reduced flow condition with three of the six notches bypassed.

FIG. 11 is an enlarged isometric view and partial cutaway view of thegeometry of the hollow cylinder and sealing pad of FIGS. 6 and 7 shownwith two of the six notches bypassed.

FIG. 12 is an enlarged isometric view and partial cutaway view of thegeometry of the hollow cylinder and sealing pad of FIGS. 6 and 7 shownin the lowest flow condition with all flow passing through the sixnotches and interconnecting channels on each cylinder face in series.

FIG. 13 is a schematic cross-sectional view of the valve assembly inaccordance with another embodiment of the invention.

FIG. 14 is an enlarged cross-sectional view of a portion of the valveassembly where indicated in FIG. 13 and showing a restrictor assembly.

FIG. 15 is an enlarged isometric view and partial cutaway view of thegeometry of the hollow cylinder and sealing pad shown removed from thevalve assembly of FIGS. 13 and 14 for purposes of clarity and shown inthe open-most condition.

DETAILED DESCRIPTION

The present invention is directed toward flow control valves. In thefollowing description, numerous specific details are provided, such asparticular valve configurations, to provide a thorough understanding ofand an enabling description for embodiments of the invention. Those ofordinary skill in the art, however, will recognize that the inventioncan be practiced without one or more of the specific details explainedin the following description. In other instances, well-known structuresor operation are not shown or described in detail to avoid obscuringaspects of the invention.

One aspect of the invention is directed to a flow control valve forproviding a substantially constant flow of fluid through the valve. Anaspect of the valve is to provide a substantially wide range of flowrate set points. In one embodiment, the valve includes a valve body witha series of concentric bores and an end cap with an inlet in the end capand an outlet in the valve body. The body contains a piston movablydisposed in a piston bore and a shaft with a spool-shaped portionmovably displaced in a second, third and fourth bore that are bothconcentric to the piston bore. A first flow passageway is providedbetween the inlet and a first restriction in a variable restrictorassembly, which share inlet fluid pressure (P1). The restrictor assemblyis comprised of a first sealing pad with a hole in the center thatslides over a face of a restrictor, and the face contains a notchedopening. The sealing pad is urged against the face with a sealing padspring. The notched opening is axially displaced relative to the sealingpad by moving the shaft's spool portion, which is powered by a handleturning a power screw. Another passageway is provided down stream of thefirst restriction and upstream of a mating cone-shaped pin and seat,which share intermediate fluid pressure (P2). The cone-shaped pin issupported in the center of the piston with its shank concentric to theround opening in the seat, which is attached to the end of the shaft. Anoutlet passageway is provided down stream of the mating pin and seat tothe outlet of the valve, which shares outlet fluid pressure (P3).

A dynamic seal is positioned proximate to the piston and piston bore andseparates the first passageway (with fluid pressure P1) from the secondpassageway (with fluid pressure P2). The dynamic seal defines a firsteffective area. The valve also includes a biasing member configured tourge the piston in a first direction toward the first passageway (P1).The inside diameter of the seat defines a second effective area which issubstantially smaller than the first effective area.

In one aspect of this embodiment, the valve is configured so thatchanges in pressure drop across the valve do not generally affect theflow rate of the fluid passing through the valve. In another aspect ofthis embodiment, the valve further includes an adjustable throttlingmember formed by the variable restrictor assembly comprised of the firstrestriction. The urging of the movably disposed piston and pin, whichmates with the seat, creates a force balance across the piston thatgoverns the pressure drop across the throttling member, which in turnmaintains substantially constant flow with substantially large pressuredrop fluctuations across the valve. The throttling member can be movableto vary the size of the opening in the first restriction. The movementof the shaft's distal end portion that creates a change in this openingalso changes the force setting of the biasing member on the P2 side ofthe piston. The double purpose of the shaft's movement creates asubstantially wide range of flow rate set point because, at the lowestflow rate, the smallest hole in the first restriction is exposed, and atthis set point the lowest pressure drop across the first restrictionexists.

FIG. 1 is an isometric view of valve assembly 100 for controlling theflow of a fluid in accordance with one embodiment of the invention. FIG.2 is an enlarged schematic cross-sectional view of the valve assembly100 taken substantially along lines 2-2 of FIG. 1. FIG. 3 is an enlargedschematic cross-sectional view of a portion of the valve assembly 100where indicated in FIG. 2. The valve assembly 100 includes a valve body102 and an inlet cap 108 that contains an inlet fitting 106 with anaperture defining a flow inlet 104. The valve body 102 contains anoutlet fitting 110 with an aperture that defines a flow outlet 111.

As best seen in FIG. 2, the valve body 102 contains a series ofconcentric bores common to longitudinal axis X1 that contain the piston112, a piston biasing member 114, and a central shaft 125 with a spoolportion 126. Attached to the lower end of the shaft 125 and axiallyaligned with the shaft is a seat 128 with a round inside diameter thatmates with a cone-shaped end 119 a of a pin 118 supported by the piston112. A pin retainer 122 sitting atop the piston 112 centers the pin 118and provides a shoulder 123 a for a mating shoulder 119 b of the pin 118against which to slide. A pin spring 116 between the pin 118 and thepiston 112 provides a force to keep the pin shoulder 119 b in contactwith the shoulder 123 a and centered to the seat 128. The spring 116also prevents the pin from “crashing” against the seat, as described inU.S. Pat. No. 4,893,649, which is hereby incorporated in its entiretyherein by reference thereto. The movement of the piston 112 and the pin118 along the longitudinal axis X1 relative to the seat 128 isconfigured to maintain a constant fluid flow rate through the valveassembly 100 despite changes in the pressure drop across the valve 100,as described below in detail.

A cup seal 124 is attached to the piston 112 and sealably engages thepiston bore 130. The cup seal 124 separates fluid within the valveassembly's flow path, so inlet pressure (P1) is on one side of the cupseal (e.g., below the cup seal) and fluid at an intermediate pressure(P2) is on the other side of the cup seal (e.g., above the cup seal). Asdiscussed below, the fluid at intermediate pressure P2 is within aseries of passageways down stream of a variable restrictor assembly 132(discussed below). In other embodiments, the cup seal 124 could besubstituted with an “O” ring or other sealing member, such as a bellowsor diaphragm.

The piston 112 and pin 118 are urged away from the seat 128 along thelongitudinal axis X1 with the biasing member 114. In the illustratedembodiment, the biasing member 114 is a stack of disk springs, but otherbiasing devices, such as a coil spring mechanism, can be used to providea biasing force against the piston 112 away from the seat 128. Thearrangement of the spring-biased piston and pin mating with the seat 128maintains substantially constant flow through the valve 100 independentof the pressure drop across the valve 100 assembly because the piston,pin and seat 128 maintain a substantially constant pressure drop acrossthe variable restrictor assembly 132.

The constant flow configuration independent of the valve's outletpressure (P3) is demonstrated by the force balance equation:P1(A _(piston))=P2(A _(piston) −A _(seat))+K _(spring) *X _(spring)+Sealdrag−(P2−P3)A _(seat)Where:A_(piston)=area enclosed by the piston bore 130A_(seat)=effective area enclosed by the inside diameter of the seat 118K_(spring)=spring constant of the biasing member 114Seal drag=drag of seal 124X_(spring)=spring deflection of the biasing member 114

The effective area A_(seat) is enclosed by the mating inside diameter ofthe seat 128 and the cone-shaped end 119 a of the pin 118.

The lower portion of the piston bore 130 below the cup seal 124 isconnected to a flow passageway 170 formed by a hole drilled in the body.The flow passageway 170 carries fluid at pressure P1 from the inlet tothe variable restrictor assembly 132. As best seen in FIGS. 2-5, thevariable restrictor assembly 132 of the illustrated embodiment includesan inlet sealing pad portion 141, a restrictor 143, and an outletsealing pad portion 145. The inlet sealing pad portion 141 includes asealing pad 136 a pressed against the restrictor 143 by a biasingmember, such as a pad springs 140 a. The pad spring 140 a pressesagainst a pad cap 142 a, which is securely screwed into a threadedaperture in the valve body 102.

In the illustrated embodiment, the restrictor 143 includes a hollowcylinder 134 in the form of a sleeve fixed to the shaft 125 around thespool portion 126. The hollow cylinder 134 has a flat surface 135 aagainst which the sealing pad 136 a presses. In the illustratedembodiment, the sealing pad 136 a is urged along lateral axis X2 towardthe first flat surface 135 a on the hollow cylinder 134 by the padsprings 140 a, which pushes on a pad pusher 138 a between the padsprings and the sealing pad. The pad springs 140 a can be of a springdesign such as a Belleville washer, wave washer, coil spring, or otherbiasing device. The pad pusher 138 a and the pad springs 140 a areguided by the pad cap 142 a. The sealing pad 136 a is guided along thelateral axis X2 by the body 102 and a sealing pad guide 150 a. Thesealing pad guide 150 a retains an inner seal 152 a and an outer seal154 a which prevents fluid leakage and maintains the fluid flow atpressure P1 through the flow passageway 170, the inside diameter of thesealing pad 136 a and the upstream side of the variable restrictor 143.

The hollow cylinder 134 has a second flat engagement surface 135 b. Asecond sealing pad 136 b on the outlet side of the hollow cylinder 134is pressed against the second flat surface 135 b by second pad springs140 b, a second pad cap 142 b, and a second pad pusher 138 b. The padpusher 138 b and the sealing pad 136 b are guided by a second sealingpad guide 150 b so that the sealing pad 136 b is also urged along thelateral axis x2 toward the restrictor 143.

As best seen in FIGS. 2 and 3, the fluid at pressure P1 flows from thelower portion of the piston bore 130 (FIG. 2) through the first flowpassageway 170, into a central aperture 133 d in the sealing pad 136 a,and into the restrictor 143 via a through-hole 133 a and associatedsurface restrictions on the first flat surface 135 a to control flowrate, as discussed in detail below. The fluid exits the restrictor 143via a through-hole 148 in the hollow cylinder 134 on the second flatsurface 135 b, and into a central aperture 136 d in the second sealingpad 136 b. The fluid entering the second sealing pad 136 b is at a fluidpressure P2, which is less than the fluid pressure P1. The fluid flowsfrom the second sealing pad 136 b into a second flow passageway 174,which carries the fluid to the pin 118 and the seat 128 at the bottomportion of the shaft 125 (FIG. 2).

In the illustrated embodiment, the through-hole 148 on the outlet sideis larger than the through-hole 133 a on the inlet side, so surfacerestrictions on the second flat surface 135 b are not needed for flowrate control. Because the restriction of through-hole 148 is quite smallcompared to the full flow condition of through-hole 133 a, the pressuredown stream of the through-hole 133 a in the cavity 172 (FIG. 3) createdbetween the inside of the hollow cylinder 134 and outer surface of thespool portion 126 and in the second sealing pad 136 b is pressure P2.Because there is no meaningful pressure drop across the through-hole148, additional seals are not needed around the second pad guide 150 b.In other embodiments, however, seals may be provided around the secondpad guide 150 b similar to the seals 152 a and 154 a discussed above. Inthe illustrated embodiment, the fluid moving through the restrictor 143is also blocked from migrating along the surface of the shaft 125 byupper and lower seals 156 and 158. The illustrated seals are grooveseals disposed in annular grooves formed in the exterior of the shaft125 above and below the hollow cylinder 134, such that the sealssealably engage the shaft and the valve body 102.

The fluid at pressure P2 flows through the second flow passageway 174into the upper portion of the piston bore 130 that contains the pistonbiasing member 114 and pin 118. The largest restriction in the valveassembly 100 is created by the cone-shaped end 119 a of the pin 118mating with seat 128 on the end of the shaft 125. The fluid flowsthrough the restriction between the pin 118 and the seat 128, therebycreating another drop in fluid pressure from P2 to P3. Down stream ofthe mating pin 118 and seat 128 is the common fluid pressure P3, whichis bound by the center and cross hole 175 in shaft 125, the seals 156and 159 between the shaft and the valve body, and the outlet fitting110, such that the pressure of the fluid exiting the valve assembly isat pressure P3.

The hollow cylinder 134 is securely held on the shaft 125 about thespool portion 126, so that the hollow cylinder moves with the shaft as aunit along the longitudinal axis X1. In the illustrated embodiment, oneend of the hollow cylinder 134 is bound by a thrust washer 144 and snapring 146, which is anchored to the spool portion 126. The opposite endof the hollow cylinder 134 is bound by a spring 160 that urges thehollow cylinder 134 toward the thrust washer 144. The spring 160 can bea coil spring, a wave washer, Belleville washer design, or other biasingmember.

As best seen in FIG. 2, the shaft 125 with the spool portion 126 iscoupled to an adjustment handle 184 extending from the valve body 102.The handle 184 is coupled to a stem 182 and a power screw 180. When thehandle 184 is turned to adjust the flow rate through the valve assembly,the stem 182 and the power screw 180 rotate and move axially, therebycausing the spool portion 126, the cylinder 134, the snap ring 146, andthe thrust washer 144 to move as a unit axially along longitudinal axisX1. This movement of the hollow cylinder 134 results in the first andsecond flat surfaces 135 a and 135 b moving longitudinally relative tothe respective sealing pads 136 a and 136 b. Accordingly, thethrough-hole 133 a on the inlet side of the hollow cylinder 134 and thethrough-hole 148 on the outlet side also move relative to the centralapertures 133 d and 136 d in the sealing pads 136 a and 136 b, such thatall or portions of the through-hole 133 a may be exposed to the fluidflow through the sealing pad.

Controlling the axial movement of the shaft 125 and the hollow cylinder134 will control the position of the through-holes 133 a and 148relative to the sealing pads 136 a and 136 b, thereby controlling thefluid flow rate through the restrictor 143. The snap ring 146, thrustwasher 144, and spring 160 provide a means of preventing backlashbetween the hollow cylinder 134 and the spool 126 during the axialmovement. In one embodiment, the product of thrust from turning of theend of the stem 182 against the end of the shaft 125 and the frictionforces between these two surfaces cause the spool portion 126 to rotateas it moves along longitudinal axis X1. Higher pressures in the valveassembly 100 create greater forces between the shaft 125 and the end ofthe stem 182, which results in greater torque applied to the shaft. Thehollow cylinder 134 allows the spool portion 126 to rotate, preventingthe spool torque from overcoming the torque that the sealing pads 136 aand 136 b exert on the hollow cylinder 134, which in turn allows thesealing pads 136 a and 136 b to maintain contact with their mating flatsurfaces 135 a and 135 b on the hollow cylinder 134. If the sealing pads136 a and 136 b were to lose contact with the mating flat surfaces 135 aand 135 b respectively, the exposed flow area of the variable restrictorassembly 132 would dramatically increase causing an undesirable increasein the flow rate set point.

FIG. 4 and FIG. 5 show an enlarged isometric view of the sealing pad 136a mating with the flat surface 135 a on the inlet side of the hollowcylinder 134, wherein only half of the sealing pad 136 a is shown forillustrative purposes. The footprint of the inside diameter of thesealing pad's central aperture 133 d is shown as dashed line 133 drelative to the through-hole 133 a. In the illustrated embodiment, theflat surface 135 a of the hollow cylinder 134 also has a blind V-shapednotch 133 b and a blind trench 133 c recessed therein and coupled to thethrough-hole 133 a. The trench 133 c is configured to receive and directfluid from the sealing pad's central aperture 133 d to the notch 133 b,and the notch directs the fluid into the through-hole 133 a.

The hollow cylinder 134 is shown in FIG. 4 in a fully open positionbecause the entire through-hole 133 a is directly exposed to the sealingpad's central aperture 133 d and fluid flowing there through. For thisopening, the maximum spring tension in disk springs 114 (FIG. 2) exists,creating the maximum pressure drop through the through holes 133 a and133 b, producing the maximum flow rate set point for the valve assembly100.

The sealing pad 136 a and hollow cylinder 134 are illustrated in FIG. 5in a lower flow rate set point because a flange portion of the sealingpad 136 a around the central aperture 133 d is positioned to cover theentire through-hole 133 a. In this position, only a portion of theV-shaped notch 133 b and the trench 133 c are within the footprint ofthe central aperture 133 d and directly exposed to fluid flow therethrough. Accordingly, fluid will enter the exposed portions of the notch133 b and the trench 133 c and will flow through the restriction createdby the sealing pad 136 a on the flat surface 135 a over the notch 133 b,and into the covered through-hole 133 a for passage through the hollowcylinder 134. The through-hole 133 a, the notch 133 b, and the trench133 c are configured so that the fluid flow rate through the inlet sideof the hollow cylinder 134 is directly related to how much of thetrench, notch, and/or through-hole is within the footprint of thesealing pad's central aperture 133 d and thereby directly exposed to thefluid flow there through. Accordingly, less exposed area of thetrench/notch/through-hole provides a lower flow rate through the inletside of the hollow cylinder, and more area exposed provides a greaterflow rate. At the lower flow rate set point shown in FIG. 5, the minimumspring tension in disk springs 114 (FIG. 2) exists, creating the minimumpressure drop through the through hole 133 b producing a lower flow rateset point than shown in FIG. 4. In other embodiments, such as thosedescribed below with reference to FIGS. 8-12, the restrictor 143 canhave different configurations of trenches and/or notches to providerestrictions to fluid flow depending on the position of the shaftrelated to the sealing pads 136 a and 136 b.

FIG. 6 is a cross-sectional view of a valve assembly 100 in accordancewith another embodiment, and FIG. 7 is an enlarged cross-sectional viewof a portion of the valve assembly where indicated in FIG. 6. The valveassembly 100 has generally the same components as those described aboveand shown in FIGS. 1-5, so only the primary differences will bediscussed. In this alternate embodiment, the restrictor 143 includes aflow restricting hollow cylinder 192 on the spool portion 126. Thehollow cylinder 192 has a through-hole 198 a in a flat surface 196 a onthe inlet side of the hollow cylinder 192. The sealing pad 136 a on theinlet side is urged against the flat surface 196 a as discussed above.The hollow cylinder 192 also has a through-hole 198 b on a flat surface196 b on the outlet side of the hollow cylinder. The sealing pad 136 bon the outlet side is urged against the flat surface 196 b in thesimilar manner. In the illustrated embodiment, the through-hole 198 a onthe inlet side has approximately the same diameter as the through-hole198 b on the outlet side. The hollow cylinder 192 includes a pluralityof flow restricting members (discussed below) on the flat surface 196 aon the inlet side and connected to the through-hole 198 a, such that theflow rate through the restrictor can be adjusted by adjusting theposition of the hollow cylinder 192 relative to central aperture 133 din the sealing pad 136 a. In at least one embodiment, flow restrictingmembers can be provided on the flat surface 196 b on the outlet side andconnected to the through-hole 198 b.

As best seen in FIGS. 8-12, the through-hole 198 a is connected to ablind V-shaped notch 200 a machined into the flat surface 196 a on theoutside of the hollow cylinder 192 on the inlet side. FIG. 9 is anenlarged isometric view of the hollow cylinder 192 showing the flatsurface 196 a, the through-hole 198 a, and the flow restricting members.These flow restricting members include a plurality of blind receptacles,referred to as trenches 202 a and 206 a, interconnected by a pluralityof blind channels 204 a. The trenches 202 a in the illustratedembodiment are radially and longitudinally offset from each other andrun generally parallel to the longitudinal axis X1. Each trench 202 a isconnected to an adjacent trench or to the through-hole 198 a by achannel 204 a, thereby forming a series of cascading flow restrictionsconfigured to allow for fluid flow through each trench in series to thethrough-hole 198 a. The trenches 202 a in the illustrated embodiment aredeeper than the connecting channels 204 a.

As best seen in FIG. 8, the hollow cylinder 192 can be positionedrelative to the sealing pad 136 a in a fully open position, so that thecentral aperture 133 d of the sealing pad 136 a and the associated fluidflow are directly over the through-hole 198 a, the V-shaped notch 200 a,and a plurality of the trenches 202 a. As the hollow cylinder 192 ismoved axially, the flat surface moves under the sealing pad 136 a sothat the flange of the sealing pad 136 a slides over and covers at leasta portion of the through-hole 198 a, the V-shaped notch 200 a, thechannels 204 a, and/or the trenches 202 a, thereby decreasing the flowrate through the inlet side of the hollow cylinder. Accordingly thechannels 204 a and the trenches 202 a are either engaged or bypassed ina series/parallel relationship with the fluid flow passing through theV-shaped notch 200 a and the through-hole 198 a.

As seen in FIG. 8, when the sealing pad 136 a and the hollow cylinder192 are in the fully open position, all of the flow bypasses thechannels 204 a and the trenches 202 a because the channels and trenchesare not covered by the sealing pad. All flow at this set point on theflat surface 196 a is restricted by the intersection of the sealingpad's central aperture 133 d and the through-hole 198 a. Thisconfiguration provides the maximum flow stroke position for the valveassembly 100 because the restriction through the inlet side of thehollow cylinder exposes the maximum possible flow area (minimum flowrestriction) with the piston springs 114 (FIG. 6) stroke position in themaximum loaded condition. This maximum flow condition can be used toclean the channels 204 a and trenches 202 a because the flow path on thehollow cylinder 192 is exposed and the maximum flow condition exists to“wash out” the flow path.

FIG. 10 is an isometric view of the sealing pad 196 a and the hollowcylinder 192 in a configuration wherein a portion of the V-shaped notch200 a, the through-hole 198 a, and approximately three of the trenches202 a are covered by the flange portion of the sealing pad 136 a. Threeof the channels 204 a are within the footprint of the central aperture133 d, and thereby bypassed from restricting the flow through the hollowcylinder. At this set point, the flow at flat surface 196 a and into thethrough-hole has a parallel path. The majority of the flow passes intothe through-hole 198 a via the exposed portion of the V-shaped notch 200a. Another portion of the flow moves through the covered trenches 202 aand channels 204 a in series after the flow from the central aperture133 d into one of the trenches 202 a that is exposed or only partiallycovered by the flange of the sealing pad 136 a. The flow then passesthrough a channel 204 a in the side of the partially covered trench 202a, then to the first completely covered trench 202 a, then the nextchannel 204 a, then to the next covered trench 202 a, and to the nextchannel 204 a where the flow enters through-hole 198 a. This “in-series”restrictive flow path of channels 204 a and trenches 202 a is a parallelpath to the flow passing through the partially exposed V-shaped notchand into the through-hole. FIG. 10 illustrates a reduced flow set pointas compared to the flow set point illustrated in FIG. 8, because lessflow area is exposed on the flat surface 196 a, and the piston springs114 (FIG. 6) are loaded less than in the position shown in FIG. 8,thereby producing a smaller pressure drop across the inlet side of thehollow cylinder.

FIG. 11 is an isometric view of the sealing pad 196 a and the hollowcylinder 192 in a configuration wherein the V-shaped notch 200 a and thethrough-hole 198 a are fully covered by the flange portion of thesealing pad 136 a. Two of the channels 204 a are bypassed and theremaining four channels and associated trenches are covered, therebyrestricting the flow through the inlet side of the hollow cylinder 192.At this set point, the flow at the flat surface 196 a has only anin-series path to the through-hole 198 a, wherein the flow passes into aportion of a trench 202 a only partially covered by the sealing pad 136a. The flow then passes through the four channels 204 a and threetrenches 202 in series. The configuration illustrated in FIG. 11provides a reduced flow set point compared to the configuration shown inFIG. 10, because there is less flow area exposed on the flat surface 196a. In addition, the piston springs 114 (FIG. 6) are loaded less than inthe position shown in FIG. 10, thereby producing a smaller pressure dropacross the inlet side of the hollow cylinder 192.

FIG. 12 is an isometric view of the sealing pad 196 a and the hollowcylinder 192 in a set point configuration wherein the V-shaped notch 200a, the through-hole 198 a, and all of the channels 204 a are fullycovered by the sealing pad. At this set point, the flow at flat surface196 a has only a series path to the through-hole 198 a where the flowpasses into an uncovered portion of the longest trench 206 a. The flowthen passes in series through the six channels 204 a and the fiveinterspersed trenches 202 a. The configuration illustrated in FIG. 12provides a reduced flow set point compared to the set point illustratedin FIG. 11, because there is less flow area exposed on the flat surface196 a, and piston springs 114 (FIG. 6) are loaded less than in theposition shown in FIG. 11, thereby producing a smaller pressure dropacross the inlet side of the hollow cylinder 192. FIG. 12 illustrates aconfiguration wherein the flow rate set point is changed entirely bychanging the tension in the piston springs 114.

As in the configurations shown in FIGS. 2-5, the sealing pad 136 b shownin FIGS. 6 and 7 on the outlet side of the hollow cylinder 192 mateswith the flat surface 196 b shown in FIG. 8. Channels 204 b, trenches202 b, and a V-shaped groove 200 b referenced in FIG. 8 aresubstantially identical to the channels 204 a, trenches 202 a, andV-shaped notch 200 a provided in the flat surface 196 a on the inletside of the hollow cylinder 192 discussed above. The channels 204 b,notches 202 a, and V-shaped groove 200 b are positioned to beselectively exposed to the central aperture 133 d in the sealing pad 136b or covered by the flange portion of the sealing pad, so as to providea variable fluid resistor 194 b that provides flow resistance to thefluid flow exiting hollow cylinder 192 and flowing into the sealing pad136 b and into the flow passageway 174 similar to the flow resistanceconfiguration on the inlet side of the restrictor.

The second fluid resistor 194 b on the outlet side can substantiallyincrease the fluid resistance for the lower flow rate set points,thereby allowing very low flow rates to be achieved with the largestcross-sectional flow passages. In the lowest flow set point, the fluidflows from the inlet pressure P1 then passes in series through part ofthe elongated trench 206 a, five trenches 202 a and the interspersed sixchannels 204 a and then into the through-hole 198 a. The flow thenpasses through the inlet side of the hollow cylinder 192, and throughthe cavity 172 created by the inside diameter of the hollow cylinder andthe outside diameter of the recessed spool portion 126. From the cavity172, the flow passes out the through-hole 198 b, then through sixchannels 204 b and the interspersed five trenches 202 b, all in series,and then into the central aperture 133 d in the sealing pad 136 b. Thecombined effect of the channels and trenches on the hollow cylinder isto produce a sequence of multiple flow restrictions in series that stepsthe fluid pressure down from P1 to P2. In other embodiments, there couldbe as few as one trench 202 a and one channel 204 a or more than fivetrenches 202 a and channels 204 a on flat surface 196 a. Likewise therecould be more or less trenches 202 b and channels 204 b on flat surface196 b. The fluid resistance for a restrictor 194 a can be, but does nothave to be, substantially identical to the resistor 194 b.

The embodiment illustrated in FIGS. 6 and 7 include seals 152 b and 154b adjacent to the sealing pad 136 b and the pad guide 150 b. Theseadditional seals help prevent leaks out of cavity 172 through the endsof the hollow cylinder 192 into cavity 172 which is at fluid pressureP2, thereby preventing an inadvertent bypass of any of the six fluidresistors that make up fluid resistor 194 b.

FIGS. 13 and 14 are cross-sectional views of another embodiment of thevalve assembly 100. In this embodiment, the sealing pads 136 a and 136 bare pressed into direct engagement with the shaft 125, rather thanagainst the hollow cylinder 192 discussed above. In this embodiment, theshaft has an aperture 266 extending there through between the sealingpads 136 a and 136 b. Accordingly, this portion of the shaft engaged bythe sealing pads 136 a and 136 b does not rotate when the handle 184and/or power screw 180. FIG. 15 is an enlarged isometric view of thesealing pad 136 a mating with the surface 262 a on the inlet side of theshaft 125. In this figure a series of notches and channels are providedon the surface of the shaft 125, similar to those illustrated in FIG. 9and discussed above, but the aperture 266 passes completely through theshaft. The aperture 266 can communicate with a series of cascadingnotches and channels in the shaft adjacent to the sealing pad on theoutlet side of the restrictor.

From the foregoing, it will be appreciated that specific embodiments ofthe invention have been described herein for purposes of illustration,but that various modifications may be made without deviating from thespirit and scope of the invention. Accordingly, the invention is notlimited except as by the appended claims.

We claim:
 1. A constant-flow valve assembly, comprising: a body with afluid inlet, a fluid outlet, a fluid passageway therebetween, and apiston chamber in fluid communication with the fluid passageway thefluid passageway containing fluid at first, second and third fluidpressures, wherein the third fluid pressure is less than the secondfluid pressure, and the second fluid pressure is less than the firstfluid pressure; a piston slidably disposed in the piston chamber and avalve assembly coupled to the fluid passageway and being configured toautomatically adjust valve position in response to the first, second orthird fluid pressures to provide a substantially constant fluid flowfrom the fluid outlet substantially independent of the pressuredifferentials between the second and third fluid pressures; and arestrictor assembly with the fluid passageway extending therethrough,the restrictor assembly having a first sealing pad, a second sealingpad, and a restrictor with a fluid pathway extending therebetween, thefirst sealing pad being positioned to receive fluid at the first fluidpressure from a first portion of the fluid passageway and to direct thefluid to the restrictor, and the second sealing pad being positioned toreceive fluid from the restrictor and direct fluid to a second portionof the fluid passageway at the second fluid pressure, the restrictorbeing axially movable to adjust the position of the fluid pathway toadjust a fluid flow rate of fluid through the fluid pathway to thesecond portion of the fluid passageway, wherein the restrictor has anouter surface, the fluid pathway includes a restrictor entry portiondefined by a plurality of blind notches interconnected by at least oneblind channel and in fluid communication with a through hole, therestrictor being movable to allow the first sealing pad to interferewith at least a portion of the restrictor entry portion to adjustablyrestrict the fluid flow into the blind notches, blind channel, orthrough hole and to control the fluid flow rate through the adjustablerestrictor assembly.
 2. The assembly of claim 1 wherein the restrictorcomprises a sleeve with an interior area and a central member disposedin the interior area, the fluid pathway extends through the sleeve andaround the central member.
 3. The assembly of claim 1, furthercomprising an external adjustment device coupled to the restrictorassembly, the adjustment device being manipulatable to move therestrictor assembly to change the position of the restrictor relative tothe first sealing pad.
 4. A constant-flow valve assembly, comprising: abody with a fluid inlet, a fluid outlet, a fluid passagewaytherebetween, the fluid passageway having a first portion containingfluid at a first fluid pressure, a second portion containing fluid at asecond fluid pressure less than the first fluid pressure; and anadjustable restrictor assembly between the first and second portions ofthe fluid passageway, the restrictor assembly having an inlet portion,an outlet portion, and a restrictor with a fluid pathway extendingtherebetween, the inlet portion being positioned to receive fluid at thefirst fluid pressure from the first portion of the fluid passageway andto direct the fluid to the restrictor, and the outlet portion beingpositioned to receive fluid from the restrictor and direct fluid to thesecond portion of the fluid passageway at the second fluid pressure, therestrictor having an entry portion and an exit portion of the fluidpathway, the restrictor being movable adjust the position of the entryand exit portions relative to the inlet and outlet portions to adjust afluid flow rate of fluid through fluid pathway to the second portion ofthe fluid passageway, wherein the restrictor has an outer surface, thefluid pathway includes the entry portion defined by a plurality of blindnotches interconnected by at least one blind channel and in fluidcommunication with a through hole, the restrictor being movable to allowthe inlet portion to interfere with at least a portion of the entryportion to adjustably restrict the fluid flow into the blind notches,blind channel, or through hole and to control the fluid flow ratethrough the adjustable restrictor assembly.
 5. The assembly of claim 4,further comprising an external adjustment device coupled to therestrictor assembly, the adjustment device being manipulatable to movethe restrictor assembly to change the position of the restrictorrelative to the inlet portion.
 6. A constant-flow valve assembly,comprising: a first fluid passageway configured to carry fluid at afirst fluid pressure; a chamber having at least a portion configured toreceive fluid at a second fluid pressure less than the first fluidpressure; a second fluid passageway connected to the portion of thepiston chamber and configured to carry fluid at the second fluidpressure; and an adjustable restrictor assembly between the first andsecond fluid passageways, the restrictor assembly having an inletportion, an outlet portion, and a restrictor with a fluid pathwayextending therebetween, the inlet portion being positioned to receivefluid at the first fluid pressure from the first fluid passageway and todirect the fluid to the restrictor, and the outlet portion beingpositioned to receive fluid from the restrictor and direct fluid to thesecond fluid passageway at the second fluid pressure, the restrictorhaving an entry portion and an exit portion of the fluid pathway, therestrictor being movable to adjust the position of the entry and exitportions relative to the inlet and outlet portions to adjust a fluidflow rate of fluid through fluid pathway to the second fluid passageway,wherein the restrictor has an outer surface, the fluid pathway includesthe entry portion defined by a plurality of blind notches interconnectedby at least one blind channel and in fluid communication with a throughhole, the restrictor being movable to allow the inlet portion tointerfere with at least a portion of the entry portion to adjustablyrestrict the fluid flow into the blind notches, blind channel, orthrough hole and to control the fluid flow rate through the adjustablerestrictor assembly.
 7. The assembly of claim 6 wherein the restrictoris movable so at least a portion of the through hole remains uncoveredand at least one blind notch adjacent to the through hole is fullycovered, whereby the through hole receives a fluid simultaneously inparallel from the covered blind notch and directly from the inletportion.
 8. The assembly of claim 6 wherein the restrictor includes anexterior surface with the entry portion thereon, and the inlet portionincludes a body segment with an aperture in fluid communication with thefirst fluid passageway and with the entry portion, the body segmentengaging the exterior surface of the restrictor body so at least aportion of the aperture is in direct fluid communication with the entryportion.
 9. The assembly of claim 6, further comprising an externaladjustment device coupled to the restrictor assembly, the adjustmentdevice being manipulatable to move the restrictor assembly to change theposition of the restrictor relative to the inlet portion.
 10. Theassembly of claim 6 wherein the restrictor has an outer surface, thefluid pathway includes the exit portion defined by at least one a blindnotch in the outer surface and in fluid communication with a throughhole, the restrictor being movable to allow the outlet portion tointerfere with at least a portion of the exit portion to adjustablyrestrict the fluid flow into through the restrictor and to control thefluid flow rate through the adjustable restrictor assembly.
 11. Aconstant-flow valve assembly, comprising: a body with a fluid inlet, afluid outlet, a fluid passageway therebetween, the fluid passagewayhaving a first portion containing fluid at a first fluid pressure, asecond portion containing fluid at a second fluid pressure less than thefirst fluid pressure; and an adjustable restrictor assembly between thefirst and second fluid passageways, the restrictor assembly having aninlet portion, an outlet portion, and a restrictor with a fluid pathwayextending therebetween, the inlet portion being positioned to receivefluid at the first fluid pressure from the first fluid passageway and todirect the fluid to the restrictor, and the outlet portion beingpositioned to receive fluid from the restrictor and direct fluid to thesecond fluid passageway at the second fluid pressure, the restrictorhaving an entry portion and an exit portion of the fluid pathway, therestrictor being movable to adjust the position of the entry and exitportions relative to the inlet and outlet portions to adjust a fluidflow rate of fluid through fluid pathway to the second fluid passageway,wherein the restrictor has an outer surface, the fluid pathway includesthe entry portion defined by a plurality of blind notches interconnectedby at least one blind channel and in fluid communication with a throughhole, the restrictor being movable to allow the inlet portion tointerfere with at least a portion of the entry portion to adjustablyrestrict the fluid flow into the blind notches, blind channel, orthrough hole and to control the fluid flow rate through the adjustablerestrictor assembly.
 12. A constant-flow valve assembly, comprising: afirst fluid passageway with fluid at a first fluid pressure; a chambercontaining fluid at a second fluid pressure less than the first fluidpressure; a second fluid passageway connected to the chamber andcontaining fluid at the second fluid pressure; a restrictor assemblybetween the first and second fluid passageways, the restrictor assemblyhaving a first sealing pad, a second sealing pad, and a restrictor witha fluid pathway extending therebetween, the first sealing pad engagingthe restrictor and being positioned to receive fluid at the first fluidpressure from the first fluid passageway and to direct the fluid to therestrictor, and the second sealing pad engaging the restrictor and beingpositioned to receive fluid from the restrictor and direct fluid to thesecond fluid passageway at the second fluid pressure, the restrictorbeing movable relative to the first and second sealing pads to adjustthe position of the fluid pathway relative to the inlet and outletportions, wherein the restrictor has an outer surface, the fluid pathwayincludes the entry portion defined by a plurality of blind notchesinterconnected by at least one blind channel and in fluid communicationwith a through hole, the restrictor being movable to allow the firstsealing pad to interfere with at least a portion of the entry portion toadjustably restrict the fluid flow into the blind notches, blindchannel, or through hole and to control the fluid flow rate through theadjustable restrictor assembly.
 13. The assembly of claim 12 wherein therestrictor comprises a sleeve with an interior area and a central memberdisposed in the interior area, the fluid pathway extends through thesleeve and around the central member.
 14. The assembly of claim 12,further comprising an external adjustment device coupled to therestrictor assembly, the adjustment device being manipulatable to movethe restrictor assembly to change the position of the restrictorrelative to at least one of the first and second sealing pads.
 15. Theassembly of claim 4 wherein the fluid passageway includes a thirdportion containing fluid at a third fluid pressure less than the secondfluid pressure, and the assembly further contains an adjustable flowrestriction between the second and third portions of the fluidpassageway and configured to provide a substantially constant fluid flowto the third portion of the fluid passageway substantially independentof the pressure differentials between the second and third fluidpressures, the adjustable flow restriction comprising a piston moveablerelative to the body, a piston biasing member engaging the piston andhaving a piston biasing tension, and a biased valve member coupled tothe piston and the fluid passageway.
 16. The assembly of claim 6,further comprising a third fluid passageway configured to carry fluid ata third fluid pressure less than the first and second fluid pressures; apiston slideably disposed in the chamber, and a biased valve memberhaving a valve seat adjacent to the third passageway, a valve body, afirst biasing member connected to the piston and having a piston biasingtension, and a second biasing member engaging the valve body, the firstbiasing member urging the piston away from the valve seat, and the valvebody being urged by the second biasing member toward the valve seat andconfigured to provide a substantially constant fluid flow to the thirdpassageway past the valve seat substantially independent of the pressuredifferentials between the second and third fluid pressures.
 17. Theassembly of claim 11 wherein the fluid passageway has a third portioncontaining fluid at a third fluid pressure less than the second fluidpressure, and the assembly further comprising an adjustable valve memberin the fluid passageway and configured to provide a constant fluid flowrate from the fluid outlet independent of pressure differentials betweenthe first, second and third fluid pressures, the adjustable valve memberhaving a piston slidably disposed in the body, a first biasing memberengaging the piston and having a piston biasing tension, a valve seatadjacent to the fluid passageway, a valve body coupled to the piston,and a second biasing member urging the valve body toward the valve seat.18. The assembly of claim 12, further comprising: a third fluidpassageway with fluid at a third fluid pressure less than the first andsecond fluid pressures; a piston slideably disposed in the chamber; anda biased valve member having a valve seat adjacent to the thirdpassageway, a valve body, a first biasing member coupled to the pistonand having a piston biasing tension, and a second biasing memberengaging the valve body, the first biasing member urging the piston awayfrom the valve seat, the valve body being urged by the second biasingmember toward the valve seat and configured to provide a substantiallyconstant fluid flow to the third passageway past the valve seatsubstantially independent of the pressure differentials between thesecond and third fluid pressures.